Underlayer Material for Photoresist

ABSTRACT

A method includes providing a layered structure on a substrate, the layered structure including a bottom layer formed over the substrate, a hard mask layer formed over the bottom layer, a material layer formed over the hard mask layer, and a photoresist layer formed over the material layer, exposing the photoresist layer to a radiation source, developing the photoresist layer, where the developing removes portions of the photoresist layer and the material layer in a single step without substantially removing portions of the hard mask layer, and etching the hard mask layer using the photoresist layer as an etch mask. The material layer may include acidic moieties and/or acid-generating molecules. The material layer may also include photo-sensitive moieties and crosslinking agents.

PRIORITY DATA

The present application is a continuation of U.S. patent applicationSer. No. 16/915,421, filed Jun. 29, 2020, which is a continuation ofU.S. patent application Ser. No. 15/903,796, filed Feb. 23, 2018, eachof which is incorporated by reference herein in its entirety.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapidgrowth. In the course of IC evolution, functional density (i.e., thenumber of interconnected devices per chip area) has generally increasedwhile geometry size (i.e., the smallest component (or line) that can becreated using a fabrication process) has decreased. This scaling downprocess generally provides benefits by increasing production efficiencyand lowering associated costs. However, such scaling down has also beenaccompanied by increased complexity in design and manufacturing ofdevices incorporating these ICs, and, for these advances to be realized,similar developments in device fabrication are needed.

In one exemplary aspect, photolithography is a process used insemiconductor micro-fabrication to selectively remove parts of a thinfilm or a substrate. The process uses light to transfer a pattern (e.g.,a geometric pattern) from a photomask to a light-sensitive layer (e.g.,a photoresist layer) on the substrate. The light causes a chemicalchange (e.g., increasing or decreasing solubility) in exposed regions ofthe light-sensitive layer. Baking processes may be performed beforeand/or after exposing the substrate, such as in a pre-exposure and/or apost-exposure baking process. A developing process then selectivelyremoves the exposed or unexposed regions with a developer solutionforming an exposure pattern in the substrate. Finally, a process isimplemented to remove (or strip) the remaining photoresist from theunderlying material layer(s), which may be subjected to addition circuitfabrication steps. For a complex IC device, a substrate may undergomultiple photolithographic patterning processes.

Structures and compositions of photoresist materials have been modifiedin order to accommodate complex patterning processes for devices withdecreased sizes. Though such modifications have been generallybeneficial, they have not been entirely satisfactory. For these reasonsand others, additional improvements are desirable.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIGS. 1A-1B illustrate a flowchart of an exemplary method according tovarious aspects of the present disclosure.

FIGS. 2-3 and 8A-14 are fragmentary cross-sectional views of anexemplary workpiece at intermediate steps of an exemplary methodaccording to various aspects of the present disclosure.

FIGS. 4-7 are schematic representations of exemplary chemical structuresaccording to various aspects of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the disclosure.Specific examples of components and arrangements are described below tosimplify the present disclosure. These are, of course, merely examplesand are not intended to be limiting. For example, the formation of afirst feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

In addition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.Moreover, the formation of a feature on, connected to, and/or coupled toanother feature in the present disclosure that follows may includeembodiments in which the features are formed in direct contact, and mayalso include embodiments in which additional features may be formedinterposing the features, such that the features may not be in directcontact. In addition, spatially relative terms, for example, “lower,”“upper,” “horizontal,” “vertical,” “above,” “over,” “below,” “beneath,”“up,” “down,” “top,” “bottom,” etc. as well as derivatives thereof(e.g., “horizontally,” “downwardly,” “upwardly,” etc.) are used for easeof the present disclosure of one features relationship to anotherfeature. The spatially relative terms are intended to cover differentorientations of the device including the features. Still further, when anumber or a range of numbers is described with “about,” “approximate,”and the like, the term is intended to encompass numbers that are within+/−10% of the number described, unless otherwise specified. For example,the term “about 5 nm” encompasses the dimension range from 4.5 nm to 5.5nm.

The present disclosure relates generally to IC device manufacturing and,more particularly, to device patterning processes using a multi-layer(e.g., a tri-layer) structure. The tri-layer structure may include aphotoresist layer, a middle layer (e.g., a hard mask layer), and abottom layer (e.g., bottom anti-reflective coating, or BARC) formed on asubstrate has demonstrated advantages in minimizing substratereflectivity of a light (e.g., radiation) source and increasing etchingselectivity between the bottom layer and the hard mask layer. However,improvements in the tri-layer structure for advanced patterningprocesses are still desired. For example, it has been observed thatformation of the hard mask layer (e.g., by chemical vapor deposition, orCVD) may introduce chemical moieties that can alter solubility of thephotoresist layer during developing process, leading to formation ofdefects and scums in the resulting pattern. As demonstrated byembodiments below, incorporating an additional thin film between thephotoresist layer and the hard mask layer serves to remedy these andother adverse effects, thus improving the quality of the photoresistlayer during the lithography patterning process. Furthermore, the thinfilm contemplated in the present disclosure also provides benefits suchas improved adhesion between the photoresist layer and the hard mask.

FIGS. 1A-1B illustrate a flowchart of a method 100 for patterning aworkpiece 200 according to some aspects of the present disclosure. Themethod 100 is merely an example, and is not intended to limit thepresent disclosure beyond what is explicitly recited in the claims.Additional operations can be provided before, during, and after themethod 100, and some operations described can be replaced, eliminated,or moved around for additional embodiments of the process. Intermediatesteps of the method 100 are described with reference to cross-sectionalviews of the workpiece 200 as shown in FIGS. 2-3 and 8-14, whileschematic representations of exemplary chemical structures are shown inFIGS. 4-7. For clarity and ease of explanation, some elements of thefigures have been simplified.

Referring to block 102 of FIG. 1A and to FIG. 2, a workpiece 200including a substrate 202 is provided (or received) for patterning. Thesubstrate 202 may comprise an elementary (single element) semiconductor,such as silicon and/or germanium; a compound semiconductor, such assilicon carbide, gallium arsenic, gallium phosphide, indium phosphide,indium arsenide, and/or indium antimonide; an alloy semiconductor suchas SiGe, GaAsP, AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP; anon-semiconductor material, such as soda-lime glass, fused silica, fusedquartz, and/or calcium fluoride (CaF₂); and/or combinations thereof.

The substrate 202 may be a single-layer material having a uniformcomposition; alternatively, the substrate 202 may include multiplematerial layers having similar or different compositions suitable for ICdevice manufacturing. In one example, the substrate 202 may be asilicon-on-insulator (SOI) substrate having a semiconductor siliconlayer formed on a silicon oxide layer. In other example, the substrate202 may include a conductive layer, a semiconductor layer, a dielectriclayer, other layers, and/or combinations thereof.

The substrate 202 may include various circuit features formed thereonincluding, for example, field effect transistors (FETs), metal-oxidesemiconductor field effect transistors (MOSFETs), CMOS transistors, highvoltage transistors, high frequency transistors, bipolar junctiontransistors, diodes, resistors, capacitors, inductors, varactors, othersuitable devices, and/or combinations thereof.

In some embodiments where the substrate 202 includes FETs, various dopedregions, such as source/drain regions, are formed on the substrate 202.The doped regions may be doped with p-type dopants, such as phosphorusor arsenic, and/or n-type dopants, such as boron or BF₂, depending ondesign requirements. The doped regions may be planar or non-planar(e.g., in a fin-like FET device) and may be formed directly on thesubstrate 202, in a P-well structure, in an N-well structure, in adual-well structure, or using a raised structure. Doped regions may beformed by implantation of dopant atoms, in-situ doped epitaxial growth,and/or other suitable techniques.

Referring to block 104 of FIG. 1A and to FIG. 2, a bottom layer 204 isformed on the substrate 202. In many embodiments, the bottom layer 204is a bottom anti-reflective coating (BARC) whose composition is chosento minimize reflectivity of the light source implemented during exposureof a subsequently-formed photoresist layer (e.g., photoresist layer 214in FIG. 8A) formed over the bottom layer 204. The bottom layer 204 maybe formed by spin-coating amorphous carbon onto a top surface of thesubstrate 202 (or a top surface of the topmost material layer of amulti-layer substrate 202) and subsequently baked for curing.

Referring to block 106 of FIG. 1A and still to FIG. 2, a hard mask layer206 is formed over the bottom layer 204. The hard mask layer 206 may bea single-layer structure or may include a number of layers, each ofwhich may include a dielectric, a metal, a metal compound, and/or othersuitable material. In many embodiments, the hard mask layer 206comprises a dielectric material such as a semiconductor oxide, asemiconductor nitride, a semiconductor oxynitride, and/or asemiconductor carbide material. In an exemplary embodiment, the hardmask layer 206 comprises silicon carbide, silicon nitride, siliconoxycarbide, silicon oxynitride, or other suitable dielectric materials.The composition of the hard mask layer 206 is chosen such that the hardmask layer 206 can be selectively etched without substantially etchingthe bottom layer 204. In other words, the hard mask layer 206 and thebottom layer 204 comprise materials having distinct etchingsensitivities towards a given etchant. The hard mask layer 206 may beformed by any suitable process including chemical vapor deposition(CVD), low-pressure CVD (LPCVD), plasma-enhanced CVD (PECVD), physicalvapor deposition (PVD), atomic layer deposition (ALD), spin-on coating,and/or other suitable techniques, and may be formed to any suitablethickness.

In the depicted embodiment, the hard mask layer 206 is formed bydepositing a dielectric material as described above by a CVD process.Specifically, the deposition process utilizes a precursor materialcomprising a combination of the following elements: silicon, nitrogen,carbon, hydrogen, oxygen, and other suitable elements. In an exemplaryembodiment, the precursor material comprises SiH₂N₂(C_(x)H_(y)). Duringthe deposition process the precursor material may produce basic moieties208 as reaction by-products, which subsequently remain in the hard masklayer 206. Non-limiting examples of the basic moieties include amines(e.g., —NH₂, —NHR, or combination thereof), sulfonium amines (e.g.,—SO₂NH₂, —SO₂NHR, or combination thereof), alkalines (e.g., NaOH, KOH,Ca(OH)₂, Mg(OH)₂, or combinations thereof), —CONH₂, —CONHR, —CSNH₂,—C=CNH₂, —C═CNHR, pyridine-NH₂, phenyl-NH₂, pyrrole-NH₂, thiophene-NH₂,or other suitable basic moieties, where R represents an alkyl, an aryl,a substituted alkyl, a substituted aryl, a heteroaromatic ring, aheteroatom, a cyclic group, or a substituted cyclic group. In manyembodiments, the basic moieties 208 outgas during the deposition of thehard mask layer 206 and accumulate at a top surface of the hard masklayer 206.

Referring to block 108 of FIG. 1A and to FIG. 3, a material layer (e.g.,a coating or a film) 210 is formed over the hard mask layer 206. In manyembodiments, the material layer 210 comprises one or more polymericmaterials and has a thickness between about 30% and about 70% of athickness of the hard mask layer 206. In many embodiments, the materiallayer 210 has a thickness between about 10% and about 35% of thethickness of the bottom layer 204. In an exemplary embodiment, thethickness of the material layer 210 is between about 40 angstrom toabout 250 angstrom. A solution of the material layer 210 (e.g.,dissolved in one or a mixture of solvents) may be spin-coated over thehard mask layer 206. In an exemplary embodiment, the solution of thematerial layer 210 employed for the spin-coating process at block 108has a lower viscosity than a solution of the bottom layer 204 employedfor the spin-coating process at block 104.

Referring to FIG. 4, the material layer 210 includes a polymer 302having a backbone 304. The backbone 304 may comprise one of anacrylate-based polymer, a poly(norbornene)-co-maleic anhydride (COMA)polymer, a poly(hydroxystyrene) (PHS) polymer, other suitable polymers,or combinations thereof. In an exemplary embodiment, the backbone 304includes poly(methyl methacrylate) (PMMA). In some embodiments, at leastone functional group 212 is attached to the backbone 304. The functionalgroup 212 may be an acidic moiety and may include at least one of acarboxylic acid (Formula I) or a benzoic acid (Formula II) whosechemical structures are depicted below. In another example, thefunctional group 212 may include a sulfonic acid group (not shown). Inan exemplary embodiment, the functional group 212 neutralizes the basicmoieties 208 of the hard mask layer 206 prior to forming the photoresistlayer 214 (FIG. 8A). Alternatively or additionally, the polymer 302includes other functional groups (e.g., photosensitizers) bonded to thebackbone 304 including, for example, benzene, phenol, other suitablefunctional groups, and/or combinations thereof.

The polymer 302 may comprise repeating units of one or more of thefollowing structures as illustrated below, where R1 comprises 3 to 15carbon atoms forming an alkyl group, cycloalkyl group, hydroxyalkylgroup, alkoxy group, alkoxyl alkyl group, or other suitable functionalgroups. In many embodiments, repeating units of the polymer 302 arecleavable upon a subsequent exposure and/or baking process.Advantageously, inclusion of the R1 groups depicted herein maycontribute to improved adhesion between the material layer 210 and thesubsequently formed photoresist layer 214 by increasing a contact angleof the photoresist material on the material layer 210.

In addition to the polymer 302, referring to FIG. 5, the material layer210 may include a polymer 306 having a backbone 308 and a functionalgroup 310 bonded thereto. The backbone 308 may be similar to ordifferent from the backbone 304 of the polymer 302 as discussed above.The functional group 310 may be any suitable group and may include alactone functional group such as a gamma-butyrolactone. Two examples oflactone functional groups are illustrated below. In an exemplaryembodiment, functional group 212 (FIG. 4) and functional group 310 maybe bonded to the same polymer backbone (e.g., the backbone 304).

Additionally, the material layer 210 may include photo-base generators(PBGs), which, as the name suggests, generates basic moieties inresponse to an applied radiation source. In many embodiments, the basicmoieties generated by the PBGs react with the functional group 310 ofthe polymer 306 to produce acidic moieties similar to functional group212 described above. Non-limiting examples of the PBGs provided hereininclude the following structures:

Alternatively, referring to FIG. 6, the material layer 210 may include apolymer 312 different from the polymer 306 in addition to the polymer302. The polymer 312 includes a backbone 314 and functional group 316.The backbone 314 may be similar to or different from the backbone 304 asdiscussed above. The functional group 316 may be any suitable group andmay include acetal, acetonide, and/or other suitable functional group asexemplified below:

In some embodiments, as depicted in FIG. 7, the material layer 210additionally or alternatively includes one or more acid-generatingmolecules 228 such as photo-acid generators (PAGs) or thermal-acidgenerators (TAGs). The acid-generating molecules 228 differ from thepolymer 302 in that they lack functional group 212 in their structuresprior to undergoing an exposure process (e.g., exposure process of block112 to be discussed below). Instead, the acid-generating molecules 228produce functional group 212 upon being exposed to an external energysource such as radiation (e.g., a radiation source 232 as depicted inFIG. 8B to be discussed below), as in the case of a PAG, or heat, as inthe case of a TAG. As such, the method 100 may include an additionalstep of applying a radiation and/or heat source to the material layer210 in order to generate functional group 212 for neutralizing the basicmoieties 208.

An exemplary structure of a PAG prior to exposure to radiation isillustrated by Formula III and an exemplary structure of a TAG is priorto exposure to heat is illustrated by Formula IV below. Following theirrespect exposure to an external energy source, the PAG may yield astructure according to Formula V and the TAG may yield a structureaccording to Formula VI. In the depicted examples, Ra comprises 1 to 20carbon atoms and is a substituted or unsubstituted monovalenthydrocarbon group having an alicyclic hydrocarbon structure selectedfrom cyclopentyl, cyclohexyl, cycloheptyl, 4-methylcyclohexyl,cyclohexylmethyl, norbornyl, adamantyl, 2-oxocyclopentyl,2-oxocyclohexyl, 2-cyclopentyl-2-oxoethyl, 2-cyclohexyl-2-oxoethyl,2-(4-methylcyclohexyl)-2-oxoethyl,4-oxa-tricyclo[4.2.1.03,7]nonan-5-on-9-yl,2-(adamantyl-1-carbonyloxy)-4-oxa-tricyclo[4.2.1.03,7]nonan-5-on-9-yl,and 4-oxoadamantyl, Rb is hydrogen or trifluoromethyl, X is acarbonyloxy (—COO—), ether, thioether, amide, or carbonate bond, and mis an integer selected between 1 and 3. As depicted in Formulas V andVI, structures of the PAG and TAG include functional group 212 such assulfonic acid (Formula V) or carboxylic acid (Formula VI).

The material layer 210 may further include sensitizers aimed to increasethe sensitivity of the subsequently formed photoresist layer (e.g.,photoresist layer 214) to a radiation source (e.g., UV light, deep UVlight, extreme UV light, etc.) implemented during an exposure process.The sensitizers may be bonded to the backbone (e.g., backbone 304,backbone 308, and/or backbone 314) of a polymer (e.g., polymer 302,polymer 306, or polymer 312) included in the material layer 210.Alternatively or additionally, the sensitizers may be blended with othercomponents included in the material layer 210. In many embodiments, thesensitizers include a phenol, styrene, fluoride, zirconium, hafnium,tin, and/or other suitable moieties. In an exemplary embodiment, atleast 30% of the functional groups attached to the polymers of thematerial layer 210 are phenol functional groups in order to amplifysensitivities of the PAGs in the subsequently formed photoresist layerto the radiation source. In some embodiments, between about 30% andabout 70% of the functional groups attached to the polymers (e.g.,polymer 302 and/or polymer 306) are phenol functional groups.

In some embodiments, the material layer 210 includes surface-activeagents that improve adhesion with a photoresist layer (e.g., photoresistlayer 214 discussed below). In an exemplary embodiment, a contact angleof the material layer 210 ranges between about 40 degrees and about 70degrees.

Referring to block 110 in FIG. 1A and to FIG. 8A, a photoresist layer214 is formed over the material layer 210. The photoresist layer 214 mayinclude any lithographically sensitive resist material, and in manyembodiments, the photoresist layer 214 includes a photoresist materialsensitive to a radiation source (e.g., UV light, deep ultraviolet (DUV)radiation, and/or EUV radiation as depicted in FIG. 9). However, theprinciples of the present disclosure apply equally to e-beam resists andother direct-write resist materials. The photoresist layer 214 may be apositive-tone or negative-tone resist material and may have amulti-layer structure. Furthermore, the photoresist layer 214 may beimplemented with a chemical amplification (CA) resist material. In oneembodiment, a positive-tone CA resist material includes a polymericmaterial (not depicted) that becomes soluble in a developer after thepolymer is exposed to acidic moieties. Alternatively, a negative-tone CAresist material includes a polymeric material (not depicted) thatbecomes insoluble in a developer after the polymer is exposed acidicmoieties.

In many embodiments, the photoresist layer 214 comprises a polymerhaving a backbone (not shown) with a plurality of functional groups (notshown) attached thereto. The polymer backbone may be an acrylate-basedpolymer or a COMA polymer, while the functional groups may includemoieties that assist any subsequent exposure and developing processes.In one example, the functional groups may include lithographicallysensitive groups (e.g., sensitizers) such as phenol, styrene, fluoride,and/or other suitable groups. In an exemplary embodiment, approximatelybetween about 30% and about 40% of the functional groups attached to thebackbone are phenol groups.

In many embodiments, the photoresist layer 214 includes one or morephoto-acid generators (PAGs) that produce acidic moieties in response toradiation exposure. In many embodiments, the PAGs found in thephotoresist layer 214 are sensitive to radiation of a differentwavelength compared to the acid-generating molecules 228 of the materiallayer 210. In alternative embodiments, the PAGs of the photoresist layer214 may be similar to the acid-generating molecules 228 of the materiallayer 210. The photoresist layer 214 may also include aphoto-decomposable base (PDB) that, as the name suggests, decomposesbasic moieties in response to the radiation source. In some embodiments,the PDB s have different photo-sensitivity compared to the PAGs.

The photoresist layer 214 may further include a photo-decomposablequencher (PDQ) to reduce concentration of acidic moieties in regionswhere chemical changes (e.g., changes in solubility) are not desired.For a positive-tone resist material, for example, these regions mayinclude unexposed or marginally-exposed regions of the photoresist layer214 that border exposed regions. Non-limiting examples of PDQ areillustrated below. The photoresist layer 214 may also include a numberof additives such as crosslinking agents (e.g., tetramethylolglycoluril, TMGU linker, or epoxy linker), surfactant, chromophores,and/or solvents.

The photoresist layer 214 may be applied by any suitable technique, andin an exemplary embodiment, the photoresist layer 214 is applied in aliquid form using a spin-on (i.e., spin coating) technique. A spincoating process may use centrifugal force to disperse the photoresistlayer 214 in a liquid form across a surface of an underlying substrate(e.g., the material layer 210) in a uniform thickness. To facilitateapplication, the photoresist layer 214 may include a solvent, which whenremoved, leaves the photoresist layer 214 in a solid or semisolid form(e.g., a film). The solvent may be one or more of the following:propylene glycol methyl ether acetate, propylene glycol monomethylether, gamma-butyrolactone, ethyl lactate, cyclohexanone, n-butylactetate, ethyl ketone, dimethyl formamide, alcohol (e.g., isopropylalcohol or ethanol), or other suitable solvent. The solvent may bedriven off as part of the spin coating, during a settling process,and/or during a post-application/pre-exposure baking process. Thepre-exposure baking process may be implemented by any suitable equipmentsuch as, for example, a hotplate, at any temperature suitable for theparticular compositions of the photoresist layer 214 and the solventemployed.

Referring to block 111 of FIG. 1A and to FIG. 8B, the material layer 210may be exposed to a radiation source having a first wavelength 232. Inan exemplary embodiment, the exposure process at block 111 isimplemented in a flood exposure (i.e., without using a photomask). Theexposure process at block 111 may supply energy to the acid-generatingmolecules 228 of the material layer 210, thereby producing functionalgroup 212 that may subsequently neutralize the basic moieties 208remaining in the hard mask layer 206.

Referring to block 112 of FIG. 1A and to FIG. 9, the photoresist layer214 may be exposed to a radiation source having a second wavelength 216.In many embodiments, the radiation source having the second wavelength216 may be an I-line (wavelength approximately 365 nm), a DUV radiationsuch as KrF excimer laser (wavelength approximately 248 nm) or ArFexcimer laser (wavelength approximately 193 nm), a EUV radiation(wavelength between about 1 nm and about 100 nm), an x-ray, an e-beam,an ion beam, and/or other suitable radiations. The exposure process atblock 112 may be performed in air, in a liquid (immersion lithography),or in vacuum (e.g., for EUV lithography and e-beam lithography). In thedepicted embodiment, the second wavelength 216 is different from thefirst wavelength 232 implemented during the exposure process at block111. In an exemplary embodiment, the exposure process at block 112implements a photolithography technique using a photomask 220 thatincludes a pattern 218. The photomask 220 may be a transmissive mask ora reflective mask, the latter of which may further implement resolutionenhancement techniques such as phase-shifting, off-axis illumination(OAI) and/or optical proximity correction (OPC). In alternativeembodiments, the radiation source having the second wavelength 216 isdirectly modulated with a predefined pattern, such as an IC layout,without using a photomask 220 (such as using a digital pattern generatoror direct-write mode). In an exemplary embodiment, the radiation sourcehaving the second wavelength 216 is a EUV radiation and the exposureprocess at block 112 is performed in a EUV lithography system.Correspondingly, a reflective photomask may be used to pattern thephotoresist layer 214.

As depicted in FIG. 9, the exposed regions 222 of the photoresist layer214 undergo chemical changes while unexposed regions 230 remainsubstantially unchanged in chemical properties. In one example, wherethe photoresist layer 214 includes PAGs, acidic moieties 224 that may besimilar to or different form the functional group 212 (e.g., Formula V)are generated in the exposed regions 222, which in turn may alter thesolubility of the photoresist material in the presence of a subsequentlyapplied developer 226 (e.g., FIG. 10).

For a tri-layer structure without the material layer 210 in which a hardmask layer (e.g., the hard mask layer 206) is disposed between a BARClayer (e.g., the bottom layer 204) and a photoresist layer (e.g., thephotoresist layer 214), the basic moieties 208 remaining in the hardmask layer 206 can diffuse into the photoresist layer 214 and inhibitthe chemical transformation of the exposed regions 222 of thephotoresist layer 214 by neutralizing the acidic moieties 224.Consequently, such inhibition can lead to formation of scum, which istypically insoluble (i.e., may not be readily removed) in a developer(e.g., developer 226), and may in turn cause defects in the resultingpattern formed in the photoresist layer 214, particularly near aboundary between the exposed regions 222 and the unexposed regions 230.To remedy this adverse effect, the present disclosure provides theadditional material layer 210 as a barrier between the hard mask layer206 and the photoresist layer 214 to consume the basic moieties 208prior to or during the exposure process at block 112, thus preventingthe formation of scum in the photoresist layer 214. In one example, theacid-generating molecules 228 such as PAGs and/or TAGs included in thematerial layer 210 produce functional group 212, which may be an acidicmoiety, in response to an externally applied radiation or heat source(either at block 111 or during the exposure process at block 112), whichmay in turn neutralize the basic moieties 208 of the hard mask layer206. As such, the basic moieties 208 are prevented from diffusing intothe photoresist layer 214 to form defect-causing scum in the resultingpattern. In another example, the neutralization process is completedprior to the exposure processes at blocks 111 and 112 since the materiallayer 210 includes functional group 212 (e.g., an acidic moiety having astructure of Formula I or Formula II) as a component of the polymer 302.

Referring to block 114 of FIG. 1A and to FIG. 10, a developing processis performed on the workpiece 200. The developing process at block 114dissolves or otherwise removes either the exposed regions 222 in thecase of a positive-tone resist development process or the unexposedregions 230 in the case of a negative-tone resist development process.The developing process at block 114 may begin with a post-exposurebaking process. Depending on the polymer(s) included in the photoresistlayer 214, the post-exposure baking process may catalyze a reactionbetween the generated acidic moieties 224 and the polymer in thephotoresist layer 214. For example, the post-exposure baking process mayaccelerate cleaving (for positive-tone resist) or cross-linking (fornegative-tone resist) of the polymer caused by the generated acid.Following the optional post-exposure baking process, a developer 226 isapplied to the workpiece 200, thereby removing the particular regions(the exposed regions 222 or the unexposed regions 230) of thephotoresist layer 214. Suitable positive-tone developers includetetramethyl ammonium hydroxide (TMAH), KOH, NaOH, and/or other suitablesolvents, and suitable negative-tone developers include solvents such asn-butyl acetate, ethanol, hexane, benzene, toluene, and/or othersuitable solvents. In the depicted embodiment, the developer 226 is apositive-tone, basic solvent such as TMAH. In many embodiments, apost-exposure bake is performed on the workpiece 200 subsequent to thedeveloping process at block 114 to further stabilize the pattern of thephotoresist layer 214.

In some embodiments, as depicted in FIG. 11A, the material layer 210remains substantially intact following the developing process at block114. In other embodiments, as depicted in FIG. 11B, portions of thematerial layer 210 substantially dissolve in the developer 226 alongwith the exposed regions 222 of the photoresist layer 214, particularlywhen the developer 226 is a basic solvent such as TMAH. Additionally oralternatively, portions of the material layer 210 may be removed by arinsing process using de-ionized (DI) water as a rinsing agent. Infurther embodiments, portions of the material layer 210 also dissolve inthe PAGs and/or TAGs, the PBGs, the PDQs, or other components includedin the photoresist layer 214, following the exposure process at block112 and/or the developing process at block 114.

Referring to block 116 of FIG. 1B and to FIG. 12A, the photoresist layer214 may be used as an etch mask to selectively remove portions of thematerial layer 210 and the hard mask layer 206 in an etching process. Inthe depicted embodiment, the etching process at block 116 includesetching the material layer 210 and the hard mask layer 206 in a singleprocess. The pattern 218 formed in the photoresist layer 214 allowsexposed portions of the material layer 210 and the hard mask layer 206to be selectively etched. The photoresist layer 214 is subsequentlyremoved from the workpiece 200 by any suitable method. Alternatively oradditionally, as depicted in block 120 in FIG. 1B and FIG. 12B, thephotoresist layer 214 and the material layer 210 are together used as anetch mask to selectively remove portions of the hard mask layer 206 inthe etching process at block 116. As such, the etching process at block116 substantially removes the hard mask layer 206, thereby demonstratingetching selectivity for the hard mask layer 206 over the bottom layer204. The photoresist layer 214 and the material layer 210 aresubsequently removed using any suitable method.

Due to differences in composition, the material layer 210 and the hardmask layer 206 may present distinct etching sensitivities provided thatthey are of comparable thickness. In the depicted embodiment, however,the material layer 210 and the hard mask layer 206 are etched in asingle process using the same etchant and under the same etchingconditions because the material layer 210 has a thickness that is only abetween about 30% and about 70% of the thickness of the underlying hardmask layer 206. In many embodiments, the material layer 210 and the hardmask layer 206 are etched in a single process while the underlyingbottom layer 204 is not substantially etched.

In some embodiments, the material layer 210 and the hard mask layer 206are etched using any suitable method including a dry etching process, awet etching process, other suitable etching process, a reactive ionetching (RIE) process, or combinations thereof. In an exemplaryembodiment, a dry etching process is implemented and employs an etchantgas that includes a fluorine-containing etchant gas (e.g., NF₃, CF₄,SF₆, CH₂F₂, CHF₃, and/or C₂F₆), an oxygen-containing gas (e.g., O₂), achlorine-containing gas (e.g., Cl₂, CHCl₃, CCl₄, SiCl₄, and/or BCl₃), abromine-containing gas (e.g., HBr and/or CHBr₃), an iodine-containinggas, other suitable gases and/or plasmas, or combinations thereof. In anexemplary embodiment, the etching process at block 116 is implementedusing a fluorine-based etchant gas for a duration of between about 4seconds and about 30 seconds.

Referring to block 118 of the FIG. 1B and to FIG. 13, portions of thebottom layer 204 (i.e., the BARC layer) are selectively removed in anetching process at block 118 using the hard mask layer 206 and thematerial layer 210 together (FIG. 12A) or the hard mask layer 206 alone(FIG. 12B) as an etch mask. The etching process at block 118demonstrates etching selectivity for the bottom layer 204 over theunderlying substrate 202. The material layer 210 and the hard mask layer206 are subsequently removed from the workpiece 200 by any suitablemethod.

In some embodiments, the bottom layer 204 is etched using any suitablemethod including a dry etching process, a wet etching process, othersuitable etching process, an RIE process, or combinations thereof. In anexemplary embodiment, a dry etching process is implemented and employsan etchant gas that includes a fluorine-containing etchant gas (e.g.,NF₃, CF₄, SF₆, CH₂F₂, CHF₃, and/or C₂F₆), an oxygen-containing gas(e.g., O₂), a chlorine-containing gas (e.g., Cl₂, CHCl₃, CCl₄, SiCl₄,and/or BCl₃), a bromine-containing gas (e.g., HBr and/or CHBr₃), aniodine-containing gas, other suitable gases and/or plasmas, orcombinations thereof. In an exemplary embodiment, the etching process atblock 118 is implemented using an oxygen-based etchant gas for aduration of between about 4 seconds and about 30 seconds.

Referring to block 120 of FIG. 1B and to FIG. 14, the substrate 202 isprocessed using the patterned bottom layer 204 as a mask. Any suitablemethod may be performed to process the substrate 202 including adeposition process, an implantation process, an epitaxial growthprocess, and/or any other fabrication process. In an exemplaryembodiment, the substrate 202 is etched using the patterned bottom layer204 as an etch mask. In some embodiments, the substrate 202 is etchedusing any suitable method including a dry etching process, a wet etchingprocess, other suitable etching process, an RIE process, or combinationsthereof. However, it is understood that the concepts of the presentdisclosure apply to any fabrication process performed on the substrate202. In various examples, the processed substrate 202 is used tofabricate a gate stack, to fabricate an interconnect structure, to formnon-planar devices by etching to expose a fin or by epitaxially growingfin material, and/or other suitable applications. The bottom layer 204is subsequently removed using any suitable method after the substrate202 is processed.

Referring to block 122 of FIG. 1B, the workpiece 200 may then beprovided for additional fabrication processes. For example, theworkpiece 200 may be used to fabricate an integrated circuit chip, asystem-on-a-chip (SOC), and/or a portion thereof, and thus thesubsequent fabrication processes may form various passive and activemicroelectronic devices such as resistors, capacitors, inductors,diodes, metal-oxide semiconductor field effect transistors (MOSFET),complementary metal-oxide semiconductor (CMOS) transistors, bipolarjunction transistors (BJT), laterally diffused MOS (LDMOS) transistors,high power MOS transistors, other types of transistors, and/or othercircuit elements.

Although not intended to be limiting, one or more embodiments of thepresent disclosure provide many benefits to a semiconductor device and aformation process thereof. For example, embodiments of a material layerformed between a hard mask layer and a photoresist layer acts as achemical barrier for consuming and/or removing chemical impuritiesproduced during film-forming processes. Impurities such as basicmoieties released during deposition of the hard mask layer may beneutralized prior to or during subsequent exposing and developing of thephotoresist layer, thus preventing the formation of defects in theresulting pattern. Furthermore, the material layer provided herein mayalso improve stability of the photoresist layer with respect to itsunderlying layers by improving properties such as adhesion of thephotoresist layer.

In one aspect, the present disclosure provides a method that includesproviding a substrate, forming a hard mask layer over the substrate,forming a first material layer over the hard mask layer, forming aphotoresist layer over the first material layer, exposing thephotoresist layer to a radiation source according to a pattern,developing the photoresist layer, and performing a first etching processto form the pattern in the first material layer and the hard mask layerbut not in the substrate. In some embodiments, forming the hard masklayer produces a basic moiety. In some embodiments, forming the firstmaterial layer produces an acid moiety that neutralizes the basic moietyproduced by the forming of the hard mask layer. In some embodiments, athickness of the first material layer is between about 30% and 70% thatof the hard mask layer.

In some embodiments, the provided method further includes forming asecond material layer over the substrate prior to the forming of thehard mask layer, and performing a second etching process using thepattern formed in the first material layer and the hard mask layer as anetch mask to form the pattern in the second material layer. In someembodiment, the second material layer is a bottom anti-reflectivecoating (BARC).

In some embodiments, the acidic moiety of the first material layerincludes one of carboxylic acid or benzoic acid, and wherein the firstmaterial layer includes a polymer having the acidic moiety bonded to itsbackbone. In further embodiments, the polymer of the first materiallayer further includes a lactone group bonded to its backbone. In stillfurther embodiments, developing of the photoresist layer removesportions of the photoresist layer and the first material layer.

In some embodiments, the provided method further includes exposing thefirst material layer to an energy source prior to the exposing of thephotoresist layer, where the first material layer includes anacid-generating molecule responsive to the energy source.

In another aspect, the present disclosure provides a method thatincludes providing a layered structure on a substrate, the layeredstructure including a bottom layer formed over the substrate, a hardmask layer formed over the bottom layer, and a coating formed over thehard mask layer, forming a photoresist layer over the coating, exposingthe photoresist layer to a radiation source, developing the photoresistlayer to form a pattern, and etching the hard mask layer using thephotoresist layer as an etch mask. In some embodiments, the exposing ofthe photoresist layer generates acidic moieties in the photoresistlayer. In some embodiments, the developing also removes portions of thephotoresist layer and the coating without substantially removingportions of the hard mask layer.

In some embodiments, the coating includes a polymer having one of acarboxylic acid or a benzoic acid attached to its backbone. In furtherembodiments, the polymer includes one of an acetal group or an acetonidegroup bonded to its backbone.

In some embodiments, the provided method further includes, prior toexposing of the photoresist layer, exposing the coating to an energysource, wherein the coating includes one of a photo-acid generator(PAG), a thermal-acid generator (TAG), or a photo-base generator (PBG).In further embodiments, the exposing of the coating is implemented usingan energy source having a wavelength different from that of the exposingof the photoresist layer.

In yet another aspect, the present disclosure provides a method thatincludes forming a bottom anti-reflective coating (BARC) over asubstrate, forming a hard mask layer over the BARC, forming a materiallayer over the hard mask layer, forming a photoresist layer over thematerial layer, performing a first exposure process, performing a secondexposure process, developing the photoresist layer to form a patter,performing a first etching process of the material layer and the hardmask layer using the photoresist layer as an etch mask, and performing asecond etching process of the BARC using the hard mask layer as an etchmask.

In some embodiments, the material layer includes a first acid-generatingmolecule sensitive to radiation having a first wavelength, and thephotoresist layer includes a second acid-generating molecule sensitiveto radiation having a second wavelength. In further embodiments, theperforming of the first exposure process is implemented using radiationof the first wavelength, and the performing of the second exposureprocess is implemented using radiation of the second wavelength. In someembodiments, the developing of the photoresist layer removes portions ofthe material layer.

In some embodiments, the forming of the hard mask layer produces a basicmoiety. In some embodiments, the performing of the first exposureprocess includes performing a flood exposure. In further embodiments,the performing of the first exposure process produces a first acidmoiety in the material layer but not in the photoresist layer.

In some embodiments, the forming of the material layer is implemented bya spin-coating process. In some embodiments, a thickness of the materiallayer is between about 30% and about 70% of a thickness of the hard masklayer. In further embodiments, a thickness of the material layer isbetween about 10% and about 35% of a thickness of the BARC.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method comprising: forming a hard mask layer ona substrate; forming a material layer on the hard mask layer, whereinthe material layer includes a first acid-generating molecule sensitiveto radiation having a first wavelength; forming a photoresist layer onthe material layer, wherein the photoresist layer includes a secondacid-generating molecule sensitive to radiation having a secondwavelength; performing a first exposure process on the material layerand the photoresist layer, wherein the performing of the first exposureprocess is implemented using radiation of the first wavelength;performing a second exposure process on the material layer and thephotoresist layer, wherein the performing of the second exposure processis implemented using radiation of the second wavelength; and developingthe photoresist layer to form a patterned photoresist layer.
 2. Themethod of claim 1, wherein the performing of the first exposure processon the material layer and the photoresist layer includes performing aflood exposure process on the material layer and the photoresist layer.3. The method of claim 1, wherein the forming of the hard mask layer onthe substrate produces a basic moiety, and wherein the performing of thefirst exposure process on the material layer and the photoresist layerincludes the material layer producing an acidic moiety such that theacidic moiety neutralizes the basic moiety.
 4. The method of claim 1,wherein the performing of the second exposure process on the materiallayer and the photoresist layer includes using a photomask.
 5. Themethod of claim 1, further comprising developing the photoresist layerto form a patterned photoresist layer, and wherein the patternedphotoresist layer includes a first feature spaced apart from a secondfeature of the patterned photoresist layer, wherein a portion of thematerial layer extends continuously from the first feature to the secondfeature after the developing of the photoresist layer to form thepatterned photoresist layer.
 6. The method of claim 1, furthercomprising developing the photoresist layer to form a patternedphotoresist layer, and wherein the patterned photoresist layer includesa first feature spaced apart from a second feature of the patternedphotoresist layer, wherein a top surface of the hard mask layerextending between the first feature and the second feature is exposedafter the developing of the photoresist layer to form the patternedphotoresist layer.
 7. The method of claim 1, further comprising formingan anti-reflective coating layer on the substrate, and wherein theforming of the hard mask layer on the substrate includes forming theanti reflective coating layer on the anti-reflective coating layer.
 8. Amethod comprising: forming a first material layer over a substrate;forming a second material layer over the first material layer, whereinthe second material layer includes a basic moiety; forming a thirdmaterial layer directly on the second material layer, wherein the thirdmaterial layer includes an acidic moiety that neutralizes the basicmoiety of the second material layer upon the forming of the thirdmaterial layer directly on the second material layer; forming aphotoresist layer over the third material layer; and patterning thephotoresist layer.
 9. The method of claim 8, wherein a concentration ofthe basic moiety accumulates at a top surface of the second materiallayer after the forming of the second material layer over the firstmaterial layer.
 10. The method of claim 8, wherein the forming of thesecond material layer produces the basic moiety.
 11. The method of claim8, wherein the basic moiety includes a material selected from the groupconsisting of amine material and an alkaline material.
 12. The method ofclaim 8, wherein the first, second and third materials are formed ofdifferent materials, and wherein the third material has a smallerthickness than the first and second material layers.
 13. The method ofclaim 8, wherein third material layer includes a polymer having abackbone with a material bonded to the backbone, the material selectedfrom the group consisting of carboxylic acid and benzoic acid.
 14. Themethod of claim 8, wherein third material layer includes a polymerhaving a backbone with a lactone group bonded to the backbone.
 15. Themethod of claim 8, wherein third material layer includes a polymerhaving a backbone with a material bonded to the backbone, the materialselected from the group consisting of acetal and acetonide.
 16. A methodcomprising: forming a first material layer over a substrate; forming asecond material layer over the first material layer, wherein the formingof the second material layer produces a basic moiety; forming a thirdmaterial layer over the second material layer; performing a treatmentprocess on the material layer that causes the third material layer toproduce an acidic moiety that neutralizes the basic moiety produced bythe forming of the second material layer over the first material layer;and forming a photosensitive layer over the third material layer. 17.The method of claim 16, wherein the performing of the treatment processoccurs after the forming of the photosensitive layer over the thirdmaterial layer.
 18. The method of claim 16, wherein the third materiallayer includes a material layer selected from the group consisting of aphoto-acid generator and a thermal-acid generator.
 19. The method ofclaim 16, wherein the first material layer includes a carbon-containingmaterial, and wherein the second material layer includes asilicon-containing material.
 20. The method of claim 16, wherein thetreatment process includes a thermal treatment process that causes thethird material layer to produce the acidic moiety.